The aim of this work is to develop
a sliding mode control scheme
to keep the operation of a flash distiller in the feasible operating
region. Flash distillation is characterized as a simple single-phase
separation system but operationally complex because it has a strong
nonlinear behavior due to the thermodynamic equilibrium, obligatory
to reach the required component separation. Control of flash distillation
processes must guarantee a good performance and robustness to achieve
preseparation quality before entering to next fractional distillation
processes. A phenomenological-based semiphysical model is used here
to represent the flash distillation process. The proposed control
structure tries to avoid the biggest problem of the flash distiller:
its recurrent restart due to temperature disturbances in the feed
flow. The suggested control schemes, applied to a given separation,
allow regulation of the pressure and the liquid level of the flash
drum, keeping also the concentration of propylene glycol at the flash
vapor outlet near its set point, rejecting temperature disturbances.
The simulation results show the features of the proposed controllers,
which overcome some of the disadvantages of typical flash distiller
controllers operating in design conditions.